Membrane-based electrodes for flow-injection determination of noble metal ions

Two types of polyvinyl chloride (PVC) membrane-based electrodes were prepar ed and studied under the flow-injection (FI) conditions in order to develop high-performance electrochemical sensors for noble metal ions. The first t ype of electrodes was similar to a classical PVC-model, whereas in the seco nd, the PVC-matrix was modified by carbon powder and sensor had no internal filling solution. As ion-sensing components (recognition elements), a seri es of O, N, S containing mono- and dibenzo-crown ethers were tested. The st rong dependence of the electrochemical signal to silver(I) ions as well as to acido-complexes of Au(III), Pd(II), Pt(IV) and Ir(IV) on the chemical st ructure of a membrane-immobilized macrocyclic ligand was found, for both gr oups of the electrodes. It was clearly shown that the response characterist ics of composite membrane-based electrodes (CMEs), having carbon powder wit hin the PVC-matrix, exhibit higher selectivity to noble metal ions than the electrodes of a conventional type. It was also recognized that such electr odes might operate as bifunctional sensors in FI potentiometric/amperometri c detection of Au(III) or Ir(IV). The response mechanism of CMEs was discus sed and the role of both chemically active agents and carbon species in the forming of resulting signals was clarified.